Evidence for two pulses of glaciation during the late Proterozoic in northern Utah and southeastern Idaho

MAX D. CRITTENDEN, JR.* u.s. Geological Survey. Menlo Park. Cal(lornia 94025 NICHOLAS CHRISTIE-BLICK Exxon Produclion Research Co .. P.o. Box 2189. How·lOn. Texas 77001 PAUL KARL LINK Deparlmelll olGeologl'. Idaho Slale Universily. Pocalello. Idaho 83029

ABSTRACT Correlation of the allochthonous, miogeo­ tochthonous structural settings (center right clinal glacial deposits with the single glacial edge in Fig. I) are parts of thin and locally A record of glaciation during late Prot­ unit present in autochthonous and parau­ deposited sequences in which mUltiple un­ erozoic time is preserved in a number of tochthonous platform sites is uncertain, but conformities attest to interruptions of sedi­ localities extending from the Sheep rock our interpretation of sedimentary facies and mentation, whereas most occurrences in the Mountains, Utah, to Pocatello, Idaho, and paleogeography suggests that only the allochthon (A in Fig. I) are parts of thicker from the Park City area 40 km east of Salt younger of the two episodes recorded in the sequences in which deposition apparently Lake City to the Deep Creek Range along allochthon is represented by the diamictites continued without major tectonic distur­ the Utah-Nevada line. Over much of this of the autochthon. bance into Cambrian time. In the au­ area, the glacial deposits and associated tochchthon, glacial sediments I accumulated rocks thicken westward and form the basal INTRODUCTION above thick trough deposits of Proterozoic part of a miogeoclinal wedge that accumu­ Y age or were deposited directly on crystal­ lated near the late Proterozoic and early Since Hintze (1913) and Blackwelder line basement of Archean and early Proter­ Paleozoic continental margin. In the east, (1910, 1925, 1932) first described them, the ozoic age. In the allochthon, similar and such deposits are thin and rest on Archean distinctive boulder-bearing black diamic­ apparently correlative glacial deposits are basement or rocks of Proterozoic Y age; in tites of northern Utah and southeastern intercalated with thick non-glacial sedi­ the west, they are part of thicker sequences Idaho have been ascribed alternately to gla­ ments and locally with submarine volcanic in which deposition apparently continued cial (Calkins and Butler, 1943; Crittenden rocks. In many areas, the base of these without significant interruption from late and others, 1952) and non-glacial processes allochthonous sections either is not exposed Proterozoic into Cambrian time. In many (Condie, 1967; Schermerhorn, 1974). The or is cut out by thrusts, but locally these places, the original continuity between the most recent studies by Varney (1976), Blick rocks unconformably overlie units of Pro­ western and eastern parts of the deposi­ (1979), and Ojakangas and Matsch (1980) terozoic X age not present within the tional wedge has been obscured by thrusting have provided definitive evidence of glacial autochthon. of Cretaceous and early Tertiary age that activity in the form of striated and faceted In the autochthon, and in some areas carried the thick basinal sequences eastward clasts, dropstones, isolated sand and gravel of the Charleston-Nebo allochthon (in over those deposited on the continental clots, and a striated glacial pavement. American Fork Canyon, for example) only platform. Recent mapping of Fremont Although interpretations differ as to the one unit of glacially related rocks has been Island in Great Salt Lake, the Wasatch details of paleogeographic setting and depo­ recognized, although there is evidence for Range between Ogden and Brigham City, sitional mechanisms, most authors now repeated fluctuations of the ice margin dur­ and the Sheeprock Mountains shows that agree that much of the diamictite was de­ ing over-all retreat (Blick, 1979; Christie­ glacial episodes represented either by dia­ posited in a glaciomarine environment. Sim­ Blick, 1980a). In several areas in the mictite or by dropstones enclosed in fine­ ilar rocks constitute the earliest deposits of allochthon, however, two glacial episodes grained laminated beds are separated by as the late Proterozoic and early Paleozoic can be recognized, separated by a sufficient much as 1,000 m of non-glacial deposits, miogeocline in many parts of the Cordillera thickness of non-glacial deposits to suggest including black slate, alternating graywacke (Crittenden and others, 1972; Stewart, 1972; that the two episodes were separated by a and siltstone, quartzite, and conglomerate. Christie-Blick and others, 1980). time interval perhaps as long as the Pleisto­ Using reasonable sedimentation rates for The diamictites are present in many areas cene. This paper presents the evidence for such deposits and by comparison with mod­ of northern Utah and southeastern Idaho ern analogues, we infer that two episodes of (Fig. I), and it was evident some time ago lin this paper. "glacial sediments" are ones that glaciation, each probably consisting of mul­ (Crittenden and others, 1971) that the dis­ accumulate in a glacial environment as defined by tiple advances and retreats, were separated tribution of these and overlying Paleozoic Boulton and Deynoux (1981). The term "non­ by a non-glacial interval of a few hundred rocks has been modified by tectonic trans­ glacial" is applied to sediments in which no gla­ cial influence has been detected. even though thousand to a few million years' duration. port that took place during the development some may have been derived by glacial activity or of the Cordilleran fold belt (King, 1969). As may have accumulated in an environment appre­ *Deceased. November 1982. a result, the rocks exposed in eastern au- ciably influenced by glacial meltwater.

Geological Society of America Bulletin. v. 94. p. 437-450, 8 figs .. April 1983.

437 438 CRITTENDEN AND OTHERS

Figure 1. Map of northern Utah and southeastern Idaho showing extent of Precambrian rocks and localities referred to in text. (I) Willard-Paris thrust; (2) Charleston-Nebo thrust; (3) concealed trace of inferred connection between 1 and 2; (A) area of allochthon referred to in text.

this conclusion and assesses its significance for regional correlation of the upper Prot­ erozoic rocks.

GLACIAL RECORD IN THE AUTOCHTHON

Antelope Island

Antelope Island (Fig. 1) is underlain tfl Area of Figure 2 mainly by granite gneiss inferred to be of Archean or early Proterozoic age (Bryant, 1980; Bryant and Graff, 1980; Hedge and others, 1983) and assigned to the Farming­ ton Canyon Complex (Eardley and Hatch,

0> 1940a). These crystalline rocks are overlain c::'" o Q:c unconformably by little-metamorphosed rocks of Proterozoic Z age, consisting of 45 m of diamictite, 40 m of pinkish-tan­ weathering laminated dolomite, and 35 m of EXPLANATION argillite (only partly exposed). These units are in turn overlain disconformably by an PhanerozoIc (0-570m.y.) \ D '" \\' indeterminate thickness, at least several tens @...... ~ Sail Lake Cily of metres, of light tan to pale gray cobble ~ Prole,ozoic Z (570-800m.y.) ". and pebble conglomerate and quartzite, representing the basal part of the Tintic D Prole,ozoic Y (800-1600 m.y.) Quartzite (Cambrian). That coarse-grained n:;\~~ A,chean (>2500 'fly) quartzite was, we believe, correctly identi­ fied as Cambrian by Eardley and Hatch z (1940b) but later was assigned to the Pre­ cambrian Mutual Formation by Larsen (1957), and this assignment was adopted for the geologic map of Utah by Stokes (1963). More recent comparisons with units ex­ posed in the Wasatch Range in both .he allochthon and autochthon confirm Eard­ ley's identification as the Tintic Quartzite and emphasize a close relationship to the exposures in the Farmington-Bountiful sec­ tion of the Wasatch Range (between Salt Lake City and Ogden) (Fig. 1), where the Tintic Quartzite rests directly on the Far­ mington Canyon Complex without any intervening rocks of Proterozoic Z age (Crittenden, 1972). These relations indicate that the line of zero thickness for Protero­ zoic Z rocks lies between Antelope Island EVIDENCE FOR PULSES OF GLACIATION 439

and the Farmington-Bountiful section of the margin of an ice sheet that reached the port on the Willard thrust (Crittenden, the Wasatch. sea. Christie-Blick (I 980a) cited evidence of 1961; Blick, 1979). The tectonic position of Antelope Island repeated glacial fluctuations during over-all The stratigraphically lowest and thickest is uncertain. Rocks exposed there are struc­ retreat but did not find evidence of pro­ section of the formation of Perry Canyon is turally beneath the Willard thrust (Fig. I; longed periods of entirely non-glacial depo­ in the upper plate of the Willard thrust, Crittenden, 1972), but they may be structur­ sition. An obvious problem is that in the beginning just south of the mouth of Perry ally above several thrusts that crop out in postulated glaciomarine environment the Canyon (Fig. 2), where the formation con­ southwestern Wyoming (see Royse and oth­ time interval represented by any particular sists of three units. The lower and upper ers, 1975; Blick, 1979). We therefore regard hiatus is difficult to evaluate. The most that units are composed of diamictite and the Antelope Island as autochthonous or can be said is that there is no evidence that intervening unit is interbedded graywacke parautochthonous. early glacial deposits within the Mineral and siltstone (see column 5 of Fig. 4 beloW). Fork had consolidated sufficiently to yield The lower diamictite, here about 365 m Mineral Fork Area clasts of diamictite to later glacial advances. thick, rests directly on the Facer Formation. Its thickness is variable along strike, how­ Glacial rocks older than the Cambrian GLACIAL RECORD IN ever; only 2 km to the east, it is a maximum Tintic Quartzite were recognized in the Cot­ THE ALLOCHTHON of 60 m thick and is locally absent. Where tonwood area (Fig. I) by Hintze (1913) and diamicite is missing, the base of the Perry by Calkins and Butler (1943) during map­ Mouth of Perry Canyon Canyon is marked by I to 5 m of coarse ping of the Alta and American Fork mining arkosic grit that grades upward into alter­ districts. Prior to 1952, the glacial units In the northern Wasatch Range (Fig. 2), nating graywacke and siltstone. Much of were called simply "tillite" and, because of the upper plate of the Willard thrust is the lower diamictite appears massive, and the absence of clasts of the distinctive dia­ characterized by a thick sequence of little­ some may be lodgement tillite (see Boulton mictite in the base of the overlying quartz­ metamorphosed rocks of late Proterozoic and Deynoux, 1981), but intercalated lenses ite, were questionably assigned to the age (Sorensen and Crittenden, 1976), ap­ of siltstone 2 to 3 m thick indicate intermit­ Cambrian (Calkins and Butler, 1943). Fur­ parently recognized by Blackwelder as early tent intervals of non-glacial deposition. ther mapping (Crittenden and others, 1952), as 1910 (Blackwelder, 1910, 1932). Mapping Clasts are predominantly 5 to 10 em in however, showed that the diamictite, there prior to 1970 (Crittenden and others, 1971) diameter, but a few are as large as I m and named the Mineral Fork Tillite, was depos­ showed that these sections, informally re­ the largest observed is nearly 3 m long. A ited above a major unconformity in two ferred to as the Huntsville sequence, consti­ count of 100 clasts showed gneissic granite broad, shallow glacial valleys cut in the top tute a consistent set of formational units (42%) and pale quartzite (34%) to be the of the older Big Cottonwood Formation that are recognizable throughout western most abundant. Clasts of pale metarhyolite and was overlapped unconformably by both Utah and southeastern Idaho and that a (10%) are an unusual component seen only the Mutual Formation (Proterozoic Z) and diamictite-bearing unit occurs in the lower in this area; clasts of schist, basalt(?), dark the basal conglomerate of the Tintic Quartz­ part of this sequence in most places where quartzite, and carbonate rocks make up the ite (Early? and Middle Cambrian; see col. 9 the base is exposed. More recent mapping remaining 14%. Thin pods of badly altered of Fig. 4 below). These relations made it (Sorensen and Crittenden, 1976) has shown metavolcanic rocks are present locally at the clear that the diamictite is separated from that diamictite-bearing rocks, informally base of this lowest diamictite. At the top, it the overlying basal Cambrian strata by not designated the "formation of Perry Can­ is overlain abruptly by graywacke and silt­ merely one unconformity but two. Calkins's yon," are exposed almost continuously stone, although all of these rocks inter­ observation that clasts of diamictite are above the Willard thrust from the Wasatch tongue locally. absent from the base of the Tintic Quartzite front near Perry Canyon at least to Pine­ The medial part of the formation of Perry is now seen to be of no age significance. view Reservoir west of Huntsville (Fig. I), a Canyon here consists of interbedded green­ The sedimentary environment of these distance of 25 km. This mapping also ish-tan graywacke and dark gray to green­ glacial deposits (referred to as the Mineral showed that a higher strand of the thrust ish-gray siltstone. Locally, thin lenses of Fork Formation by Christie-Blick) has been repeats both the diamictite-bearing units laminated gray limestone are present at or discussed most recently by Varney (1976), and the underlying Facer Formation. Inas­ just above the lower contact. On the ridge Ojakangas and Matsch (1980, 1982), Blick much as the thrust descends stratigraphi­ south of the mouth of Perry Canyon, len­ (1979), Christie-Blick (1980a, 1982a) and cally westward, the thickest sections of both ticular beds of tan-weathering quartzitic Knoll and others (1981). Evidence of glacia­ formations are exposed near the mountain graywacke or quartzitic sandstone attain a tion includes a few dropstones, clots of sand front, where they are cut off by the Wasatch thickness of I to 2 m. To the southeast, the or gravel enclosed in finer-grained strata fault. Assuming that this descent continues, medial unit forms much of the ridge crest perhaps analogous to those described by the rocks of the upper plate are presumed to between Willard and Perry Canyons. In this Ovenshine (1970), and striae on the underly­ have been deposited west of those of the area, the dominant lithology is dark gray-to ing surface (Blick, 1979; Ojakangas and lower plate, but the distance that originally olive-drab-weathering siltstone in which Matsch, 1980). There is considerable dis­ separated them is uncertain; an estimate of even parallel bedding 3 to 5 em thick com­ agreement in detail about the interpretation 10 to 20 km appears reasonable on the basis bines with weak foliation, intersecting at an of the Mineral Fork Tillite, but most recent of change in thickness of the Facer Forma­ angle of 30° to 40°, to produce a distinc­ workers agree that it accumulated at or near tion and other evidence of the total trans- tively banded phyllite. Although poorly au

.... , ...... ~ ~? .Qu '<" t. D':::". . . . ' .... ; ...... :;...r-:':::: ,,-,....,;c,..____'' • • • • • ..~. • • •

Figure 2. Map of area at mouth of Perry and Willard Canyons, showing lower and upper diamictite in the formation of Perry Canyon (after Sorensen and Crittenden, 1976). Locality shown in Figure I. EVIDENCE FOR PULSES OF GLACIATION 441

FIGURE 2 exposed on the wooded south slope of Perry allochthonous but are in a structurally Canyon, the medial unit appears from a lower plate of the Willard thrust. EXPLANATION cross section to be about 500 m thick. In contrast to the section at the mouth of The upper part of the formation of Perry Perry Canyon, this section contains diamic­ Canyon consists of massive diamictite that tite only in lenticular pods ranging from 20 ~ forms prominent dark cliffs on the north or 30 m to perhaps 400 m thick (see columns Undifferentiated Quaternary Deposits }f slope of Perry Canyon about I km east of 6 and 7 of Fig. 4 below). In general, this LOWER PLATE OF UPPER PLATE OF the mountain front. Although the base is section shows more evidence of downslope WILLARD THRUST WILLARD THRUST cut by a fault in Perry Canyon and may movement of glacially derived sediment actually be in a separate thrust sheet, this (sliding and sediment gravity flow). In addi­ body of diamictite appears to overlie the tion, submarine volcanic rocks, including Maxfield Limestone medial unit of graywacke and siltstone and pillow basalt (Fig. 3), and shallow intrusive is overlain by laminated greenish-gray, fine­ rocks are more abundant, and a 1- to 3-m­ grained siltstone assigned to the Maple thick bed of carbonate that consists of Ophir Shale Canyon Formation (Crittenden and others, either gray laminated limestone or, more 1971). About 200 m of diamictite is exposed rarely, pinkish-tan laminated dolomite o in the cliffs, and an additional thickness of forms a "cap" over several of the diamictite Tintic Quartzite as much as '100 m is exposed on the south lenses similar to those described by Willi­ slope of the canyon. The total thickness is ams (1979) in Australia. Such caps locally approximate because of the uncertain ef­ extend beyond the limits of the diamictite fects of the fault that has been mapped fol­ lens. Although nowhere do two lenses of lowing the bottom of the stream canyon to diamictite appear one above another, as the east. The rocks above and below the two they do at the mouth of Perry Canyon, diamictites, however, are quite different, some lenses rest directly on the underlying Mutual Formation and it is unlikely that they represent a single Facer Formation or on the Willard thrust, horizon repeated by faulting. A clast count whereas others are entirely surrounded by in the upper diamictite recorded 70% gran­ non-glacial(?) deposits. Where diamictite is Inkom Formation ite and gneissic rocks, 27% quartzite, and absent, the basal bed usually is a coarse about 3% other sedimentary and igneous arkosic grit, rarely more than I m thick, rocks. consisting of angular to subrounded grains ~ N Caddy Canyon Formation .gc in a silty matrix. In many places, it is faulted <1> .0 U Willard Canyon to Pineview Reservoir out or obscured by float. Between expo­ C E <1> o :::J u sures of diamictite, the formation consists ~ ~ Papoose Creek Formation 0.. On the north rim of Willard Canyon, a of dark gray to black, thin-bedded pyritic short distance southwest of the exposures siltstone intercalated with beds of gray­ ~ just described, the formation of Perry wacke, dark gray sandstone, or locally tan­ Kelly Canyon Formation Canyon forms a second band of outcrops weathering quartzite. Pyrite is disseminated that extends almost continuously southeast in many of these rocks as cubes as large as I ~ to Pineview Reservoir about 5 km west of em across. To the southeast beyond North Maple Canyon Formation Huntsville (Fig. I). These exposures are also Odgen Pass (Fig. 4), lenses of diamictite are

~ Formation of Perry Canyon Zpd- Diamictite unit

UNCONFORMITY UNCONFORMITY x C -,"Xfc'-\""'-.-\ \ / 0•. Xf'". . • .2..0 Farmington Canyon Complex Facer Formation } ~ ct

Figure 3. Basaltic pillow from volcanic rocks inter­ calated with diamictite member of the formation of Perry Canyon, North Ogden Pass, Utah. Specimen is 14 cm long. 442 CRITTENDEN AND OTHERS

(I) (2) (3) (4) Pocatello Area Oxlard Peak Fremont Island Lillie Mountain 13km 29 km

N Upper Willard Allochthon ·s" Upper ~ "0 0: Late c ------­ .~ glacial "0 E (; ePisode LL 1iii~~~ __ 2 a;g 0 0.

>- (; N ·2" ~ ~ ~ 0. Early glacial episode

2000lt 500m

EXPLANATION Limestone or dolomite Pocatello 1I. Moonlight Mountain ~ o 0 o ~ Chinks Peak Shale 1 (I) ~ h. Siltstone , Slumping Scout ~ Mountain ~ Sandstone or graywacke r---/\.f', Unconformity [(;:=>.'SI Quartzite (1) Location of numbered column r.~~; II Conglomerate 13km Distance between sections (in parentheses .where inferred ~~~}~I Diamictite across thrust)

v • v Volcanic rocks (mainly pillow basalt) ~V v ~ Intrusive rocks ~ I I Dropstones L Graded beds

Figure 4. Columnar sections showing correlation of glacially , derived Proterozoic units in northern Utah and southeastern I Idaho.

ite and chloritoid are widespread and, par­ thinner and less abundant, and the entire stone accumulated m an environment less ticularly along the ridge between Willard unit intertongues laterally first with blue­ strongly reducing than that represented by Peak and Brigham City, are large enough to black, slaty, pyritic mudstone and this, in the diamictite, as well as one farther from form "spotted" phyllites. In a few places turn, with olive-drab siltstone and tan­ the influence of glaciers. near Willard Canyon (Fig. 2), the gray­ weathering, coarse graywacke. The absence Over much of the area, rocks of the lower wacke and sandstones show incipient devel­ of free carbon, which results in "normal" thrust plate are slaty or phyllitic and show opment of metamorphic biotite, but this is colors, suggests that the graywacke and silt- distinct foliation oblique to bedding. Chlor- recognizable only in thin section. EVIDENCE FOR PULSES OF GLACIATION 443

(5) (6) (7l (el (9) Perry Canyon Willard Canyon North Ogden Pass Antelope Island Minerai Fork (20 km) 16 km (60+ km) 30km

Lower Willard Allochthon Autochthon A

Facer Formation Limestone of Autochthon Canyon (Cambrian) Complex

Figure 4. (Continued).

/ Facer quartzite beds terminate in bulbous lobes Formation enclosed in siltstone. Locally, stacked lobes freed from the less-resistant matrix by wave suggest that successive bodies of sand came action and now form storm beaches along to rest at about the same place. This lower the northern shore of the island. Quartzite, part of the unit contains sparse dropstones, Fremont Island including a distinctive green chromian var­ consisting of rounded quartzite clasts from iety, is the next most abundant clast, and 0.5 to 2.5 m in diameter, associated with At the west face of the Wasatch Range metamorphic and volcanic rocks and lime­ sand clots, and enclosed in thin-bedded silt­ (Figs. I and 2), the Willard thrust is cut by stone form the remainder. Although the stone (Figs. 5 and 6). Although the clasts the Wasatch fault and displaced southward, giant clasts are impressive and locally form and clots are limited in number and distri­ passing beneath the Great Salt Lake be­ closely packed masses, they are rather bution, they provide unequivocal evidence tween Antelope and Fremont Islands (Crit­ widely dispersed in a dark pyritic matrix in of an episode of glacial transport and raft­ tenden, 1972). As a consequence, the west­ which the clasts are predominantly in the ing appreciably older than that recorded by ward extension of the allochthonous se­ range of I to 5 cm in diameter. This body of the massive diamictite exposed across the quence exposed in Perry and Willard Can­ diamictite is generally massive at the base northern part of the island. yons crops out on Little Mountain, Fre­ but in the upper part is distinctly bedded on The lowest units of the formation of mont Island, and nearby on the south end a scale of several metres, and it contains Perry Canyon exposed on Fremont Island of Promontory Point. As noted above, the lenses and irregular beds of slate, siltstone, consist of graded beds of coarse grit from I diamictite exposed only 10 km to the south and, locally, tuff. Several examples of drop­ to 5 m thick, intercalated with siltstone and on Antelope Island is structurally below the stones and nattened till clots were observed, mudstone (Fig. 4, column 3). Clast size in Willard thrust and therefore was deposited although fine details of sedimentary struc­ graded beds commonly ranges from coarse many tens of kilometres to the east of that ture commonly are obscured by the marked granules and small pebbles at the base to in the allochthon. foliation. This unit appears to be the same coarse sand (I mm) at the top. All beds are The most distinctive unit of the rocks as that exposed on Little Mountain to the strongly folded and locally overturned exposed on Fremont Island is a 600-m-thick east (Christie-Blick, 1980b). (Fig. 7). A few cross-beds in this unit, when section of diamictite that extends across the Beneath the prominent diamictite, and restored for tectonic tilt, suggest north­ northern ridge of the island and forms its forming the saddle across the center of the westward paleocurrents. In view of the de­ highest point (Eardley and Hatch, 1940b; island, is a unit composed predominantly of formation, however, this direction must be Condie, 1967; Blick, 1979) . .These and black slate that is strongly foliated and regarded as tentative. underlying rocks that occupy the remainder locally knotted and spotted by chloritoid of the island are here assigned to the forma­ and pyrite. A section approximately normal POCATELLO AREA, IDAHO tion of Perry Canyon (Fig. 4, column 3). to the strike indicates that the maximum Near the western point of the island, the possible thickness is on the order of 1,000 Diamictite in the Scout Mountain Mem­ diamictite intertongues with basalt nows m, but because the entire unit is internally ber of the Pocatello Formation near Poca­ and peperite and is cut by several shallow folded, the actual thickness is uncertain. tello has been attributed to glaciomarine sills. Although relict textures are well pre­ Near the top of the slate unit, there is sev­ sedimentation by all who have studied it served, the igneous rocks are altered to eral tens of metres of distinctive clastic (Ludlum, 1942; Crittenden and others, greenstone that consists mainly of chlorite, dolomite and dolomitic sandstone. 1971; Trimble, 1976; Link and others, 1980; sericite, epidote, actinolite, albite, calcite, Below the slate, there is a section of inter­ Link, 1981, 1982, 1983), on the basis of the and iron oxides. These rocks have been calated dirty quartzite, siltstone, and locally, presence of striated clasts in diamictite and searched repeatedly for material fresh greenstone. Part of it is thrown into large­ correlation with glacial rocks in northern enough to use for isotopic dating, but scale folds that are a prominent feature of Utah. Recent mapping (Link and others, without success. This diamictite is charac­ the southwest face of the island. Evidence of 1980) has shown, however, that part of the terized by large clasts of gneissic granite (as slumping and wet-sediment deformation is type section of the Pocatello Formation is much as 5 m), many of which have been also seen in several places where irregular structurally overturned, and that pyritic 444 CRITTENDEN AND OTHERS

sparsely pebbly quartzite which, if un­ faulted, is 280 m thick. A poorly exposed and lenticular interval of greenstone, brec­ cia, and porphyritic lava assigned to the Bannock Volcanic Member overlies the quartzite. These volcanic rocks are 110 m thick on Scout Mountain and thicken northward. Next above them, there is a 70- m interval of brown, thin-bedded sand­ stone, followed by the lower diamictite, which is about 100 m thick. The lower dia­ mictite is crudely bedded. and grades up­ ward into inversely to normally bedded sandstone. Five pebble counts in this dia­ mictite average 43% quartzite, 52% silt­ stone, and 5% volcanic rocks. A 150-m coarsening-upward sequence of siltstone and graded sandstone overlies the lower diamictite, culminating in 50 to 100 m of cobble and boulder conglomerate that is intercalated with trough-cross-bedded me­ dium- and coarse-grained sandstone. One pebble count in the conglomerate indicated Figure S. Dropstones, the largest 2.S m long, enclosed in dark brown-weathering 85% quartzite, II % granitic rocks, 2% silt­ siltstone in lower glacial unit, Fremont Island. stone, and 2% volcanic clasts. Quartzite and brown siltstone overlie the shale originally designated the "lower mem­ Range from Moonlight Mountain to south conglomerate and are in turn overlain by ber" by Trimble (1976) is actually part of of Oxford Peak (Fig. 4). The most complete the upper diamictite, which is more than the upper member. A revised stratigraphic section through the diamictite-bearing 150 m thick and contains clasts as much as column of the Pocatello Formation is Scout Mountain Member occurs on both 1.5 m in diameter. Striated clasts are pres­ shown in Figure 4 (column I). sides of the north-trending ridge of Scout ent, although rare. Two pebble counts in the The Pocatello Formation is exposed Mountain 20 km south of Pocatello. The upper diamictite on Scout Mountain aver­ along much of the length of the Bannock lowest exposed unit is a greenish, vitreous, age 28% quartzite, 51 % basement rock (granitic and gneissic rocks), 20% siltstone, and I % volcanic rock. A I-m-thick laterally persistent bed of laminated, pink silty dolomite caps the upper diamictite. The sec­ tion above the upper diamictite is well exposed in structurally overturned beds north of Portneuf Narrows (Fig. I), where a thinning- and fining-upward transgressive clastic and limestone sequence overlies the dolomite. The upper member of the Poca­ tello Formation is a monotonous dark gray, silver-weathering laminated and locally py­ ritic shale or argillite that is similar to the Kelley Canyon Formation of Utah and to postglacial shales (Twitya Formation) at a similar stratigraphic level in the Northwest Territories, Canada (Christie-Blick and others, 1980). On the slopes west of Chinks Peak (Fig. 4) diamictite of the Scout Mountain Mem­ ber is interbedded with and contains clasts of the Bannock Volcanic Member, which here reaches a thickness of 400 m. Both diamictite and cobble conglomerate are present southeast of Chinks Peak and in an Figure 6. Sand clot 12 cm long, inferred to have been dropped into thinly laminated isolated northern exposure on Moonlight siltstone, lower glacial unit, Fremont Island. Mountain. The diamictite is thicker at these EVIDENCE FOR PULSES OF GLACIATION 445

localities than on Scout Mountain, but structural complications preclude accurate measurement of the section. The Scout Mountain Member near Poca­ tello consists of a variety of sedimentary facies (Link, 1982, 1983). The thickest diamictite is exposed in the north on Chinks Peak and Moonlight Mountain (Fig. 4), where it is interpreted as lodge­ ment tillite or glaciomarine diamictite, in part deposited by sediment gravity flow. South of Portneuf Narrows, slope and basinal facies are present, including strata interpreted as turbidites and "contourites," mass-flow channelized conglomerate, and redeposited diamictite. The southernmost exposures at Garden Creek Gap (Fig. I) consist predominantly of shallow-marine and nearshore deposits (Thompson and Link, 1981; Thompson, 1982).

OXFORD PEAK, IDAHO

At least 450 m of diamictite, graywacke, and siltstone of the Scout Mountain Mem­ Figure 7. Folded coarse-grained graded beds below lowest glacial unit, Fremont Island. ber of the Pocatello Formation occurs on Pencil is 12 cm long. Oxford Peak (Fig. I) and in isolated hills in Cache Valley to the east. These clastic rocks overlie and are intruded by mafic subaque­ an ice sheet that reached the sea. The heter­ and others in the 1950s. Subsequent map­ ous volcanic rocks of the Bannock Volcanic ogeneous beds along the ridge south of ping by Morris and Kopf (1970a, 1970b) Member of the Pocatello Formation that Oxford Peak are interpreted as diamicton and Christie-Blick (1982b) has led to further include pillow lava, agglomerate, volcani­ deposited by sediment gravity flow and sed­ stratigraphic subdivision and recognition of clastic siltstone, and diabase sills. All are iment derived by the winnowing of diamic­ individual formations of the Huntsville metamorphosed to greenschist facies. ton, intercalated with volcanic sand and sequence of Crittenden and others (1971). The Scout Mountain Member is laterally pillow lava. A common and distinctive Diamictite occurs in two stratigraphic units, variable, in both thickness and lithology. In lithology is silt-chip diamictite with a small the lower one in the middle of the Otts its southernmost exposures at Five Mile component of quartzite or granitic clasts. Canyon Formation and the upper one in the Canyon, some 15 km southeast of Oxford The silt fragments are thought to have been overlying Dutch Peak Formation (Dutch Peak (Fig. I), it contains 250 m of massive incorporated during redeposition of diamic­ Peak "tillite" of Cohenour, 1959). The lower cobble-bearing diamictite. About I to 2 km ton on a submarine slope. diamictite is thin and lenticular and is south of Oxford Peak, it consists of 200 m separated from the thick upper body by sev­ of medium- to thick-bedded cobble diamic­ SHEEPROCK MOUNTAINS eral hundred metres of quartzite. tite, silt-chip diamictite, siltstone, and fine The lower diamictite unit is best exposed graywacke. These beds interfinger to the A thick sequence of little-metamor­ in the vicinity of Otts Canyon (Fig. 8, south with green volcaniclastic sandstone. phosed, allochthonous Proterozoic rocks, column 3), where it is from 0 to 500 m thick Near Oxford Peak, a 40-m-thick sill of including diamictite, occurs in the Sheep­ and consists of interbedded diamictite, metadiabase intrudes silt-chip diamictite rock Mountains, about 135 km south of graywacke, grit, quartzite, and slate. Under­ and extends about 10 km to the southeast. Fremont Island and 60 km west of the lying rocks consist of several hundred A generalized section is shown in column 2 Wasatch Mountains (Figs. I and 8). Several metres of gray and silver-gray, banded slate of Figure 4. major thrusts separate these rocks from and phyllite, lithologically similar to pelitic Thirteen pebble counts in diamictite on those immediately above the Willard thrust, rocks interbedded with the dia mictite, and Oxford Peak averaged 28 '1( white, gray, and but it seems likely that the rocks of Sheep­ suggestive of a conformable and perhaps brown quartzite; 10% granite and vein rock Mountains were transported about the interfingering contact. The diamictite oc­ quartz; 39% black and light gray siltstone; same dista nce eastward with respect to the curs in intervals from a few metres to sev­ 10'1( medium and coarse sandstone; and autochthon as was Fremont Island (Blick, eral tens of metres thick and is generally in 131,7c volcanic clasts, including white felsite 1979). sharp contact with adjacent slate and and dark porphyry. Proterozoic rocks were early recognized quartzite. The diamictite matrix is gray, The massive diamictite at Five Mile in the Sheeprock Mountains by Loughlin green, or black, and phyllitic; texturally, it Canyon is inferred to have been deposited (1920) and the over-all stratigraphy was is fairly homogeneous to heterogeneous with as lodgement till near the grounding line of established in mapping by Cohenour (1959) silty and gritty wisps. The concentration of 446 CRITTENDEN AND OTHERS

(I) (2) (3) (4) (5) South Sheep rock Black Crook Peak Dulch Peak Pole and Oils Canyans Mountains Deep Creek Range 7km (6 km) (5 km) (125km) (Fig. 1)

0"" ~.2 0- U O .. E :: 0 0"-

2000"1 500m /~

o 0

Figure 8. Columnar sections showing correlation of glacially derived Proterozoic units in the Sheeprock Mountains and Deep Creek Range, central and western

Utah. Lithologic symbols as in Figure 4. Index map is for o 5km Sheeprock Mountains only. Deep Creek Range is located I I in area shown in Figure I. + clasts is variable; typically these consist of Area underlain about 95% quartzite, with subordinate by diamictite quartz, dolomite, granite, and intraforma­ tional siltstone. Dolomite is locally abund­ ant, however. Clasts are predominantly 2 to 5 cm in diameter, but a few are as large as 112"30' boulders. Beneath the Pole Canyon thrust, in the vicinity of Otts Canyon, the lower diamictite unit thins abruptly toward the upper part is intruded by diabase sills. The in Fig. 8), however, the contact between the north. Above the Pole Canyon thrust, it is quartzite is typically fine to medium grained, quartzite and lower diamictite units is prob­ less than 70 m thick and pinches out toward with moderately to well-rounded and ably faulted, and the exposed thickness of the northwest. The lower diamictite is not sorted grains, and is locally vitreous. It is quartzite may be less than its true strati­ exposed south of the Indian Springs tear thin to thick bedded, commonly laminated, graphic thickness. Above the Pole Canyon fault (Fig. 8, column 4), probably because and rarely cross-bedded. Rare, angular thrust, the quartzite unit thins toward the the exposures do not extend far enough fragments of black diamictite in conglomer­ northwest and is less than 250 m thick near downsection at this locality (Blick, 1979). ate near the base confirm the stratigraphic Black Crook Peak. Between the diamictite units, and consti­ sequence and indicate that the diamictite of The upper diamictite unit, the Dutch tuting the upper member of the Otts the early glacial episode was consolidated Peak Formation, consists of as much as Canyon Formation (Fig. 8, column 3), there before the overlying beds were deposited. 1,750 m of moderately bedded to well­ are several hundred to more than 1,000 m of The quartzite interfingers with the underly­ bedded diamictite, conglomerate, gray­ gray quartzite, with subordinate interbeds ing diamictite unit and is markedly thinner wacke, grit, sandstone, quartzite, siltstone, of conglomerate and grit (especially near toward the south in rocks beneath the Pole and shale. The contact with the underlying the base), and of graywacke, slate, siltstone, Canyon thrust. Near the divide between quartzite is transitional but probably not and shale (especially near the top). The Otts and Pole Canyons (close to location 3 interfingering, because a bed of distinctive EVIDENCE FOR PULSES OF GLACIATION 447 metallic blue-gray quartzite, associated with graphic levels of diamictite with laminites bodies of diamictite or by the presence of dropstones near the base of the Dutch Peak, containing dropstones suggest that the dia­ dropstones can be correlated confidently at persists along the northern flank of the mictite was deposited by sediment gravity least within northern and central Utah. The Sheeprock Mountains for several kilome­ flow and from floating ice. Paleocurrents correlations currently proposed (Figs. 4 and tres at the same stratigraphic level. Angular estimated from the few available structures 8) are based on stratigraphic position and diabase fragments, locally included in con­ in the upper diamictite and the medial on the presence of intercalated or closely glomerate above this marker bed, were quartzite are directed toward the south­ associated volcanic rocks and, locally, of probably derived from the underlying dia­ west, perhaps approximately parallel to the carbonate rocks. They are strongly sup­ base sills or compositionally similar rocks at edge of the inferred basin. The Sheeprock ported also by unit-by-unit correlation of about the same stratigraphic level. The dia­ basin was characterized by generally oxidiz­ the overlying non-glacial formations that base fragments thus attest to local erosion ing conditions and differs in this respect constitute the remainder of the Huntsville (channels?) and to penecontemporaneous from the Perry Canyon and Mineral Fork sequence (Crittenden and others, 1971; mafic volcanism as in other parts of the basins, where conditions were reducing. Christie-Blick, 1982b). allochthon. Poorly sorted rocks of the Correlation within the Willard alloch­ Dutch Peak Formation are typically olive DEEP CREEK RANGE thon is comparatively straightforward. The green to gray, chloritic, moderately phyl­ presence of intercalated pillow basalt and litic, and mineralogically, chemically, and Metadiamictite, presumably in the west­ the distinctive underlying gray clastic dolo­ texturally heterogeneous at microscopic to ern part of the allochthon, crops out about mite permits a direct tie from the thick dia­ megascopic scales (Blick, 1979). Major clast 125 km west of the Sheeprock Mountains in mictite on Fremont Island to that exposed types are dolomite, granite, and quartzite the southern part of the Deep Creek Range on Little Mountain (Christie-Blick, 1980b). (including the rare but distinctive chromian in two units separated by about 200 m of From there to exposures in the Wasatch variety). Subordinate types include a variety quartzite (Misch and Hazzard, 1962). Bick Range, the tie is less explicit, but in the of metamorphic, igneous, and sedimentary (1966) reinterpreted the outcrop pattern in upper allochthon at Perry Canyon, the rocks. In the Sheeprock area, 29 clast terms of a single diamictite unit repeated by upper diamictite also contains thick lenses counts indicate pronounced lateral and stra­ a tight syncline, with a core of quartzite. of pillow basalt in exposures 1.5 to 2.5 km tigraphic variations in the proportions of Facing directions are difficult to determine east of the canyon mouth, whereas igneous clast types over short distances, but some from available sedimentary structures be­ rocks are thin or absent in the lower diamic­ gross generalizations can be made. Dolo­ cause the rocks are in the garnet and stauro­ tite. Correlation of the upper diamictite mite clasts are most abundant near the base lite grades of regional metamorphism with diamictite in the lower Willard alloch­ and toward the east, quartzite clasts are (Nelson, 1969) and have a strong schistose thon also is supported by pillow basalts and most common near the top and south of the fabric. Nevertheless, important lithologic mafic to intermediate intrusives present in Indian Springs fault, and igneous clasts are differences between the diamictite units that unit, particularly near North Ogden particularly common in the northwest. seem to corroborate the original interpreta­ Pass (Fig. 4, column 7). The formation of Clasts are predominantly 2 to 5 cm in tion of Misch and Hazzard (1962). The Perry Canyon as a whole thins eastward, diameter, although rarely as large as 3 m lower unit consists of sparsely pebbly schist, and the upper diamictite horizon rests (one granite gneiss and one chromian which appears to be less sandy and gritty directly on the Willard thrust in the south­ quartzite). Rocks above the Pole Canyon and better bedded than the generally more easternmost exposures in Ogden Canyon. thrust are coarsest near the base. The size of crowded pebbly diamictite of the upper unit This is to be expected from the observation largest clasts decreases stratigraphically (Christie-Blick, 1982b). Clasts, mostly the that over a larger area the Willard thrust upward and toward the south. Diamictite size of pebbles but rarely as large as I m, are rises stratigraphically eastward. and conglomerate of the Dutch Peak For­ mainly "granite" (gneissose and direction­ Correlation of the glacial units within the mation intertongue with lenticular, mature less varieties; about 70%) and quartzite allochthon from Perry Canyon and Fre­ quartzite in the upper part and in southern (about 25%). Subordinate types are other mont Island to the Sheeprock Mountains, exposures. In addition, thick, poorly sorted metamorphic, igneous, and sedimentary 135 km to the south (Fig. 8), is much more rocks pass laterally into rather thinner rocks, including marble. The interpretation difficult, even though all the major units of quartzite toward the northwest in the vicin­ of the diamictite units as glaciomarine the Huntsville sequence of Crittenden and ity of Black Crook Peak (Fig. 8, columns I (Misch and Hazzard, 1962) is tentatively others (1971) except the Maple Canyon and 2). reaffirmed on the basis of well-developed Formation can be recognized in both areas The thinning of both diamictite units and bedding and the presence of a possible (Christie-Blick, 1982b). This difficulty is the intervening quartzite toward the north­ dropstone near the top of the upper unit. reflected in the use of different names (the west and the facies change of the upper Otts Canyon and Dutch Peak Formations) diamictite to quartzite in the same direction CORRELATION OF GLACIAL for the glacial units. The Kelley Canyon suggest deposition near the edge of a locally DEPOSITS WITHIN UTAH Formation, which overlies the Maple Can­ subsiding marine embayment. The diamic­ yon in the northern Wasatch Range, rests tite is interpreted to be mainly a basinal Until recently, stratigraphic data have directly on the Dutch Peak in the Sheep­ deposit, and the quartzite to represent been inadequate to permit detailed correla­ rock Mountains. The greatest difference better-sorted shelf sand that prograded into tion of glacial deposits between any of these between the two sequences is that quartzite the adjoining basin. The bedding character­ sections of Proterozoic Z age. Mapping intervenes between the diamictite units in istics and textural heterogeneity of the dia­ described above, however, now suggests the Sheeprock Mountains, whereas gray­ mictite and the association at many strati- that the glacial episodes recorded by thick wacke and siltstone occupy this interval in 448 CRITTENDEN AND OTHERS

Perry Canyon and slate does so on Fremont allochthonous and autochthonous deposits, tite are present in the Pocatello Formation, Island. In addition, the diamictites in the and one of us (Crittenden) has observed that but they occupy a very restricted strati­ two areas are petrographically quite dis­ clasts of the distinctive green chromian graphic range and locally intertongue with tinct. On the other hand, the lower glacial quartzites are a characteristic although mi­ the volcanics. Where both diamictites are unit in both areas overlies other "basinal" nor constituent in both sections. Palinspastic present, they overlie the main mass of vol­ deposits, and the upper unit in both is asso­ restoration of the Willard thrust, however, canic rocks. Therefore, the diamictites near ciated with mafic volcanic or intrusive indicates that the sections now exposed in Pocatello are also thought to correlate with rocks. These similarities suggest that the Perry and Willard Canyons were originally only the younger of the two episodes of glacial units in the two areas may be cor­ deposited somewhere northwest of the pres­ glaciation represented in the formation of relative in spite of the differences between ent site of Antelope Island. Therefore, Perry Canyon in Utah. them. because the upper diamictite thins and Units of the Huntsville sequence have not becomes lenticular southeastward in the REGIONAL CORRELATION been recognized in the Deep Creek Range, allochthon, the diamictites on Antelope probably for the most part as a result of Island may never have been directly contin­ The general equivalence of glacial rocks lateral facies changes, but also as a result of uous with those in the allochthon. of late Proterozoic age throughout the Cor­ metamorphism and structural complica­ The Mineral Fork Tillite in the Cotton­ dillera is now widely accepted (Stewart, tions. Regardless of this problem, the tie wood area (Fig. 4, column 9) lies nearly 30 1972; Christie-Blick and others, 1980), but from the Sheeprock Mountains westward to km farther southeast and contains still in most areas, only one episode of glaciation the Deep Creek Range is perhaps more fewer clues as to possible correlation. has been recognized. In view of the evidence secure than correlations to the north and :\Ieither basic volcanic rocks nor persistent presented here for two such episodes in east. In the Deep Creek area, diamictite bedded carbonate rocks are present. More­ parts of Utah, a similar possibility needs to units are separated by mature quartzite and over, clast composition is dominated by be examined for other areas. overlain by schist that may be equivalent to quartzite and dolomite, suggesting deriva­ In the Death Valley area of California, the Kelley Canyon Formation (Fig. 8, tion from a sedimentary terrane, rather than thick bodies of diamictite in the upper column 5). Although the rocks differ in one dominated by gneiss and granite. Proterozoic Kingston Peak Formation were detail from those in the Sheeprock Moun­ Although carbonate rocks are entirely ab­ recognized long ago by Hazzard (1937), and tains, the over-all sequence is very similar. sent from the underlying Big Cottonwood it seems likely that these units are generally Correlation from the allochthon to the Formation and from the correlative Uinta correlative with the glacial deposits in Utah autochthon within Utah also remains pro­ Mountain Group that lies to the east along and Idaho described above. Nevertheless, blematic; the mafic igneous rocks, preferen­ the trend of the subglacial valleys in which although these bodies locally reach nearly tially associated with the upper diamictite the Mineral Fork was deposited, it seems 3,000 m in thickness, and in places record within the allochthon,are entirely absent in most likely that the abundant carbonate fluctuations of an ice margin (Miller, 1982), the autochthon. The capping layer of pink­ clasts in the Mineral Fork, which include detailed stratigraphic and paleogeographic ish-tan, laminated dolomite in the autoch­ oolitic and stromatolitic dolomites, were studies completed to date do not yield evi­ thonous or parautochthonous section of derived from a stratigraphically higher part dence for more than one widespread epi­ diamictite on Antelope Island (Fig. 4, of one or the other of those sequences of sode of glaciation (Wright and others, 1976; column 8), however, closely resembles the Proterozoic Y age. Such carbonate rocks Miller and others, 1981). laminated dolomites that locally overlie the are inferred to have been removed from the The southeastern part of the Mackenzie diamictites of Perry Canyon and the con­ Uinta Mountain area by erosion during late Mountains of the Northwest Territories, glomerate beds of the Maple Canyon For­ Proterozoic glaciation or prior to deposi­ Canada, is the only other area where upper mation. The closest exposure of such lam­ tion of the Cambrian and Mississippian Proterozoic strata may record two episodes inated dolomite in the allochthon is at the rocks that now overlie the rocks of the of glaciation. Eisbacher (1978) showed that south tip of Promontory Point, where it Uinta Mountain Group in the western part locally, north of the Redstone River, 15 to appears to be associated with coarse, dark­ of the rangc. 20 m of diamictite occurs at the base of the gray, granule-bearing quartzite assigned to Sayunei Formation, and it is separated the Maple Canyon Formation that may be a CORRELA TION FROM NORTHERN from the massive diamictites of the overly­ facies equivalent of diamictite. Unfortu­ UTAH TO SOUTHEASTERN IDAHO ing Shezal Formation by about 250 m of nately, the detailed stratigraphic relations of maroon siltstone (see section 7 of his Fig. these units to the rocks on Fremont Island Intercalated diamictite and mafic vol­ 10). This thickness is approximately com­ are obscured by the intervening arm of canic and shallow intrusive rocks assigned parable with that separating the diamictite Great Salt Lake. The best current inference to the Pocatello Formation and exposed units in Utah, suggesting that two pulses of is that the diamictite on Antelope Island near Oxford Peak (Fig. 4, column 2) are glaciation may be represented here also. represents a thinner shoreward equivalent correlated with the upper diamictite of the However, both Young (1976) and G. H. of the upper diamictite of the Fremont formation of Perry Canyon in the Willard Eisbacher (1980, written commun.) noted Island, Little Mountain, and Perry Canyon allochthon. The outcrops of pillow basalt, that the siltstones grade laterally into turbi­ sections. Such a correlation would be con­ volcaniclastic siltstone, and massive diamic­ dites containing abundant outsized clasts sistent with a general west-dipping paleo­ tite on Oxford Peak and near Twin Lakes believed to be dropstones. Thus, over a slope beneath the diamictite, combined with Reservoir in Cache Valley to the east are larger area, glaciation may have been rela­ onlap of basin deposits toward the east. strikingly similar to the exposures on Little tively continuous, and there is no firm basis Some support is offered also by clast lithol­ Mountain near Ogden. Near Pocatello for detailed correlation with the two glacial ogy; gneissic granite predominates in both (Fig. 4, column I), two thin units of diamic- intervals described in Utah. EVIDENCE FOR PULSES OF GLACIATION 449

PALEOGEOGRAPHIC SETTING AND have been separated by as little as 0.5 m.y. identification of tills and tillites in ancient SEDIMENTATION RATE or as much as 25 m.y. sedimentary sequences: Precambrian Re­ search, v. 15, p. 397-422. Bryant, B., 1980, Metamorphic and structural The data now available suggest that early ACKNOWLEDGMENTS history of the Farmington Canyon complex, in Proterozoic Z time, the present site of Wasatch Mountains, Utah [abs.]: Geological central Utah and adjoining parts of western The data reported here are by-products of Society of America Abstracts with Pro­ North America were situated within a con­ geologic mapping by the U.S. Geological grams, v. 12, p. 269. Bryant, B., and Graff, P., 1990, Igneous rocks on tinent that was undergoing regional exten­ Survey (Crittenden and associates in Utah Antelope Island, Great Salt Lake, Utah: sion and glaciation. Glacial deposits occur and S. S. Oriel and associates in Idaho) Geological Society of America Abstracts intermittently throughout the Cordillera beginning as early as 1950 and continuing with Programs, v. 12, p. 269. from Death Valley to Alaska (Stewart, 1972; intermittently through 1981. This research Calkins, F. Coo and Butler, B. Soo 1943, Geology Christie-Blick and others, 1980). Tongues included detailed mapping in the central and ore deposits of the Cottonwood-Amer­ ican Fork area, Utah: U.S. Geological Sur­ of ice periodically extended into the adjoin­ and northern Wasatch Range and recon­ vey Professional Paper 20 I, 152 p. ing sea and dropped their entrained debris naissance on Antelope and Fremont Islands Christie-Blick, N., 1980a, Glacial advance and on the edge of the continental platform, in the Great Salt Lake. Recent geologic retreat sequences, upper Proterozoic Min­ and in graben where it mingled with normal mapping and sedimentologic studies by eraI Fork Formation, northwestern Utah: Geological Society of America Abstracts marine sediments. Glacial deposits that Christie-Blick in the Wasatch Range, on with Programs, v. 12, p. 269. may be similar in age are present in the Fremont Island, at Little Mountain, and in 1990b, Field guide to the geology of Little southern Appalachian Mountains (Schwab, the Sheeprock Mountains, and by Link in Mountain, ill Precambrian rocks of the 1976; Rankin and others, 1969), but because southeastern Idaho were supported by Na­ northern Wasatch: Field trip number 6, no traces of late Proterozoic glaciation are tional Science Foundation Grants A TM 74- Ogden, Utah, Geological Society of America Rocky Mountain Section Meeting, 8 p. preserved in the central part of North Amer­ 24201, EAR 77-06008, and EAR 78-15194 1992a, Upper Precambrian (Eocambrian) ica, the possible extent of ice sheets across to J. C. Crowell. Responsibility for this Mineral Fork Tillite of Utah: A continental the craton cannot be determined. report is shared jointly, except for the parts glacial and glaciomarine sequence: Discus­ The best-documented lithologic ana­ dealing with the Sheeprock Mountains and sion: Geological Society of America Bul­ letin, v. 93, p. I g4-186. logues for these Proterozoic deposits are Deep Creek Range, Utah, prepared by 1982b, Upper Proterozoic and Lower from the Antarctic (Barrett, 1975; Ander­ Christie-Blick, and the section on south­ Cambrian rocks of the Sheeprock Moun­ son and others, 1981) and the Miocene eastern Idaho, prepared by Link. We are tains, Utah: Regional correlation and sig­ through Holocene deposits of the Yakataga indebted to H. Doelling, J.M.G. Miller, nificance: Geological Society of America Formation off the coast of Alaska (Plafker H. T. Morris, and L. A. Woodward for Bulletin, v. 93, p. 735-750. Christie-Blick, N., Link, P. Koo Miller, J.M.G., and Addicott, 1976). Although the latter are helpful reviews of the manuscript. Young, G. M., and Crowell, J. c., InO, inferred to be the product of alpine glacia­ Regional geologic events inferred from up­ tion along a rugged coastline rather than a per Proterozoic rocks of the North Ameri­ low-lying one, the sediments bear a close REFERENCES CITED can Cordillera: Geological Society of Amer­ ica Abstracts with Programs, v. 12, p. 402. resemblance to those of the formation of Cohenour, R. E., 1959, Sheeprock Mountains, Perry Canyon and the Mineral Fork Tillite. Anderson, J. 8., Kurtz. D. D., Domack, E. W .• and Balshaw. K. M., 1991, Antarctic glacial Tooele and Juab Counties: Precambrian and Diamictite is abundant in all sections of the marine sediments: Journal of Geology, v. gg, Paleozoic stratigraphy, igneous rocks, struc­ Yakataga, locally making up more than p.399-414. ture, geomorphology, and economic geol­ 60% of the formation. Siltstone and mud­ Barrett, P. J .. 1975, Textural characteristics of ogy: Utah Geological and Mineralogical Survey Bulletin 63, 20 I p. stone vary greatly in abundance, as in Utah. Cenozoic preglacial and glacial sediments at site 270. Ross Sea, Antarctica. ill Hayes. Condie, K. c., 1967, Petrology of the late Pre­ However, sandstone and conglomerate D. E., Frakes, L. A., and others, Initial re­ cambrian tillite(?) association in northern (outwash') appear to be more common in ports of the Deep Sea Drilling Project, Utah: Geological Society of America Bul­ the Yakataga than in the Perry Canyon, and Volume 28: Washington, D.C., U.S. Gov­ letin, v. 78, p. 1317-1343. in this respect, the Yakataga more closely ernment Printing Office. p. 757-767. Crittenden, M. D., Jr., 1961, Magnitude of thrust faulting in northern Utah: U.S. Geo­ resembles the Mineral Fork Tillite. Bick, K. F., 1966, Geology of the Deep Creek Mountains. 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